The present invention relates to an electro-optical device for emitting light from a self-emitting element by using a pixel driving circuit.
In an electro-optical device such as an organic electroluminescence (hereinafter, referred to as ‘EL’), it has been widely used a method that pixel regions emitting different color light components from each other are arranged in a matrix and light components emitted from the respective pixel regions are synthesized, such that the full color display is realized. As an example, there is a RGB method in which the pixel regions for red (R), green (G), and blue (B) are arranged side by side. The color light components emitted from the respective pixel regions depend on a light-emitting material included in a light-emitting element of each pixel region.
However, since light-emitting efficiency is different according to the type of the light emitting material used, if each pixel region emits light under the same condition, the quantity of light of a specific color is generally reduced. Thus, when light components emitted from the pixel regions are synthesized, a desired color cannot be displayed with high definition. In particular, in the case of the RGB method, three color light components are synthesized to display white light. However, when the brightness balance (that is, white balance) for displaying white is poor, the overall quality of the display device is degraded.
In this case, the light-emitting element such as the organic EL element is known to have a feature that the quantity of light is proportional to current value, and thus large current preferably needs to be supplied to the light-emitting element for emitting a large quantity of light.
However, in the organic EL element, when a large current per a unit area is needed, the light emitting material deteriorates exponentially. Accordingly, when a large current flows into a specific light-emitting element, the life span of the light-emitting element becomes short as compared to other light-emitting elements. As a result, the color irregularity is caused and the overall display device deteriorates rapidly.
As a countermeasure against these problems, a method in which the light emitting area of the light emitting region emitting the color light component having the highest light-emitting efficiency decreases as compared to the light emitting areas of the light emitting regions emitting other color light components, thereby lengthening the life span and controlling the white balance is disclosed (Patent Document 1). According to Patent Document 1, a display pixel is formed on a region surrounded by a gate signal line 51 and a drain signal line 52.
On the other hand, it has been also known that the life span of the light-emitting element (the time that brightness deteriorates) is different according to the type of the light-emitting material used. Therefore, even though the same amount of current is supplied to the respective light-emitting elements, the difference in brightness between the respective color light components occurs as the time passes, and thus the white balance is collapsed and the color irregularity is caused.
As another countermeasure against these problems, a method in which the light emitting area of the self-emitting device that represents the shortest half brightness time is made to be larger than that of the self-emitting device that represents the longest half brightness time is disclosed (Patent Document 2). According to Patent Document 2, by changing the interval of the signal lines, the area of the pixel region is changed.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2001-290441.
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2003-168561.